Needing some help putting together an itinerary for Eastern Canada! We are thinking of heading to Toronto, Ottawa, Montreal and Quebec City. Just wondering about what order would make the most sense. We will be taking a car everywhere and so transportation won't be an issue.

We are also thinking approximately 3 days in each place totalling to about 2 weeks. Any places we should focus more time on?

Where are you coming from and what month?
Transportation could become a problem if a foot of snow falls.If you just want to see the cities, you might ride ViaRail.

Sorry! We will be going in July. We will be driving. We were thinking starting in Montreal and making our way to Ottawa then Toronto, perhaps some day trips to Quebec City?

We thought that Ottawa could be a few day trips from Montreal or should we just stay in Ottawa?

You'll spend a lot of time on the road making day trips from Montreal to Ottawa as it is about 2 hours each way. The same goes for day trips from Montreal to Quebec City, which is slightly further.

I think that 3 days each in Ottawa and Quebec City would be just about right.

Driving and parking in Toronto and Montreal will be horrendous, so you should plan to use public transit when you are there to get around. The sights in Ottawa and Quebec City are fairly concentrated so you can likely walk to most places from your hotel. In Quebec City, you may want to make a day's excursion to Montmorency Falls and the Ile d'Orléans.

One caveat for Ottawa--most accommodation has been booking up quickly and prices have sky-rocketed for the week around Canada Day (1 July) for the 150th Anniversary celebrations, so if you want to visit at that time, a day trip might be the only possibility.

http://www.ottawa2017.ca/events/signature-events/

Adding to the good advice from laverendrye, the world's largest jazz festival takes over Montreal at the start of July and while it is a great time it also jams up accommodations, so make early reservations. There is some sort of celebration in Montreal nearly every summer weekend.